board: gateworks: venice: add imx8mn-gw7902 support

The GW7902 is based on the i.MX 8M Mini / Nano SoC featuring:
 - LPDDR4 DRAM
 - eMMC FLASH
 - Gateworks System Controller
 - LTE CAT M1 modem
 - USB 2.0 HUB
 - M.2 Socket with USB2.0, PCIe, and dual-SIM
 - IMX8M FEC
 - PCIe based GbE
 - RS232/RS485/RS422 serial transceiver
 - GPS
 - CAN bus
 - WiFi / Bluetooth
 - MIPI header (DSI/CSI/GPIO/PWM/I2S)
 - PMIC

To add support for the i.MX8M Nano GW7902:
 - Add imx8mn-venice dts/defconfig/include
 - Add imx8mn-gw7902 dts
 - Add imx8mn-2gb lpddr4 dram configs
 - Add misc support for IMX8M Nano SoC
 - rename imx8mm-venice.c to venice.c as it is no longer imx8mm specific
 - update README with differences for IMX8MN vs IMX8MM

Signed-off-by: Tim Harvey <tharvey@gateworks.com>
Reviewed-by: Fabio Estevam <festevam@gmail.com>
diff --git a/arch/arm/mach-imx/imx8m/Kconfig b/arch/arm/mach-imx/imx8m/Kconfig
index cc2975b..fae7049 100644
--- a/arch/arm/mach-imx/imx8m/Kconfig
+++ b/arch/arm/mach-imx/imx8m/Kconfig
@@ -99,6 +99,13 @@
 	select SUPPORT_SPL
 	select IMX8M_DDR4
 
+config TARGET_IMX8MN_VENICE
+	bool "Support Gateworks Venice iMX8M Nano module"
+	select BINMAN
+	select IMX8MN
+	select SUPPORT_SPL
+	select IMX8M_LPDDR4
+
 config TARGET_IMX8MP_EVK
 	bool "imx8mp LPDDR4 EVK board"
 	select BINMAN